# Formatted Input
Formatted Input
# Formatted Input
* * *
**[Scan Formats](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#Scan%20Formats)· [Scan Functions](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#Scan%20Functions)· [Scan Conversion Specifiers](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#Scan%20Conversion%20Specifiers)**
* * *
Several library functions help you convert data values from
text sequences that are generally readable by people to
encoded internal representations. You provide a
[format string](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#format%20string) as the value of the
`format` argument to each of these functions, hence
the term **formatted input**.
The functions fall into two categories:
The **byte scan functions**
(declared in
[``](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_stdio.html#<stdio.h>))
convert sequences of type *char* to internal representations,
and help you scan such sequences that you read:
[fscanf](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_stdio.html#fscanf),
[scanf](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_stdio.html#scanf),
and
[sscanf](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_stdio.html#sscanf).
For these function, a format string is a
[multibyte string](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_over.html#multibyte%20string)
that begins and ends in the
[initial shift state](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_charset.html#initial%20shift%20state).
The **wide scan functions**
(declared in
[``](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_wchar.html#<wchar.h>)
and hence added with
**[Amendment 1](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_over.html#Amendment%201)**)
convert sequences of type
[`wchar_t`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_stddef.html#wchar_t),
to internal representations,
and help you scan such sequences that you read:
[fwscanf](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_wchar.html#fwscanf),
[wscanf](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_wchar.html#wscanf),
and
[swscanf](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_wchar.html#swscanf).
For these functions, a format string is a
[wide-character string](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_over.html#wide-character%20string).
In the descriptions that follow, a wide character `wc`
from a format string or a stream is compared to a specific (byte)
character `c` as if by evaluating the expression
`wctob(wc) == c`.
## Scan Formats
A format string has the same general
[syntax](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#format%20string)
for the scan functions as for the
[print functions](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#Formatted%20Output):
zero or more
[conversion specifications](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#conversion%20specification),
interspersed with literal text and
[white space](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#white%20space).
For the scan functions, however, a conversion specification is one of the
[scan conversion specifications](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#scan%20conversion%20specification) described below.
A scan function scans the format string once from beginning
to end to determine what conversions to perform. Every scan
function accepts a
[varying number
of arguments](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_stdarg.html#varying%20number%20of%20arguments), either directly or under control of an argument of type
[`va_list`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_stdarg.html#va_list).
Some scan conversion specifications
in the format string use the next argument in the list.
A scan function uses each successive argument no more than
once. Trailing arguments can be left unused.
In the description that follows, the
[integer conversions](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#integer%20conversions) and
[floating-point conversions](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#floating-point%20conversions) are the same as for the
[print functions](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#Formatted%20Output).
## Scan Functions
For the scan functions, literal text in a format string must
match the next characters to scan in the input text.
[White space](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#white%20space) in
a format string must match the longest possible sequence of the next
zero or more white-space characters in the input. Except for the
[scan conversion specifier](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#Scan%20Conversion%20Specifiers)
[`%n`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#%n)
(which consumes no input), each
**scan conversion specification**
determines a pattern that one or more of the next characters in the
input must match. And except for the
[scan conversion specifiers](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#Scan%20Conversion%20Specifiers)
[`c`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#%c),
[`n`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#%n), and
[`\[`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#%[),
every match begins by skipping any
[white space](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#%n) characters in the input.
A scan function returns when:
- it reaches the terminating null in the format string
- it cannot obtain additional input characters to scan
(**input failure**)
- a conversion fails
(**matching failure**)
A scan function returns
[`EOF`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_stdio.html#EOF)
if an input failure occurs before any conversion. Otherwise it returns
the number of converted values stored. If one or more characters form
a valid prefix but the conversion fails, the valid prefix is consumed
before the scan function returns. Thus:
scanf("%i", &i) consumes 0X from field 0XZ
scanf("%f", &f) consumes 3.2E from field 3.2EZCopy to clipboard
A scan conversion specification typically converts the matched input
characters to a corresponding encoded value. The next argument value
must be the address of an object. The conversion converts the encoded
representation (as necessary) and stores its value in the object.
A scan conversion specification has the format shown in the diagram.
Support for fixed-point conversions is added with
the C Technical Report TR18037.
These closely match the extensions for the Freescale
Signal Processing Engine Auxiliary Processing Unit.
This [implementation](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_index.html#implementation)
also includes, as a conforming extension, conversions for
the vectors supported by the Freescale
**AltiVec** architecture.
Following the percent character (**`%`**)
in the format string, you can write an asterisk (**`*`**)
to indicate that the conversion should not store
the converted value in an object.
For [AltiVec](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#AltiVec) vector conversions,
you can either precede or follow an asterisk with an optional
**separator**, the characters
comma, semicolon, equal sign, or underscore. The conversion
occurs for each of the elements of the vector, and
matches a separator sequence between each pair of elements.
If you specify a separator, the separator sequence is optional
[white space](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#white%20space) ending
with the separator.
If you specify no separator, the default separator sequence is:
- for the `c` conversion specifier, nothing.
- for all other conversion specifications, optional white space
ending with a space.
Following any `*` and/or separator, you can write a nonzero
**field width**
that specifies the maximum number of input characters
to match for the conversion (not counting any
[white space](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#white%20space) that the
pattern can first skip).
## Scan Conversion Specifiers
Following any
[field width](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#scan%20field%20width),
you must write a one-character **scan conversion specifier**,
either a one-character code or a
[scan set](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#scan%20set),
possibly preceded by a one- or two-character qualifier.
Each combination determines the type required of the
next argument (if any) and how
the scan functions interpret the text sequence and converts it to
an encoded value.
The [integer](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#integer%20conversions) and
[floating-point conversions](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#floating-point%20conversions) also determine
what base to assume for the text representation. (The base is
the `base` argument to the functions
[`strtol`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_stdlib.html#strtol) and
[`strtoul`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_stdlib.html#strtoul).)
The following table lists all defined combinations and
their properties.
Conversion Argument Conversion
Specifier Type Function Base
%c char x[]
%lc wchar_t x[]
%d int *x strtol 10
%hd short *x strtol 10
%ld long *x strtol 10
%e float *x strtod 10
%le double *x strtod 10
%Le long double *x strtod 10
%E float *x strtod 10
%lE double *x strtod 10
%LE long double *x strtod 10
%f float *x strtod 10
%lf double *x strtod 10
%Lf long double *x strtod 10
%g float *x strtod 10
%lg double *x strtod 10
%Lg long double *x strtod 10
%G float *x strtod 10
%lG double *x strtod 10
%LG long double *x strtod 10
%i int *x strtol 0
%hi short *x strtol 0
%li long *x strtol 0
%n int *x
%hn short *x
%ln long *x
%o unsigned int *x strtoul 8
%ho unsigned short *x strtoul 8
%lo unsigned long *x strtoul 8
%p void **x
%s char x[]
%ls wchar_t x[]
%u unsigned int *x strtoul 10
%hu unsigned short *x strtoul 10
%lu unsigned long *x strtoul 10
%x unsigned int *x strtoul 16
%hx unsigned short *x strtoul 16
%lx unsigned long *x strtoul 16
%X unsigned int *x strtoul 16
%hX unsigned short *x strtoul 16
%lX unsigned long *x strtoul 16
%[...] char x[]
%l[...] wchar_t x[]
%% noneCopy to clipboard
The scan conversion specifier (or
[scan set](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#scan%20set)) determines any behavior
not summarized in this table. In the following descriptions,
examples follow each of the scan conversion specifiers.
In each example, the function
[`sscanf`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_stdio.html#sscanf)
matches the **`bold`** characters.
You write **`%c`**
to store the matched input characters in
an array object. If you specify no field width *w,* then *w*
has the value one. The match does not skip leading
[white space](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#white%20space). Any
sequence of *w* characters matches the conversion pattern.
sscanf("129E-2", "%c", &c) stores '1'
sscanf("129E-2", "%2c", &c[0]) stores '1', '2'Copy to clipboard
For a
[wide stream](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_file.html#wide%20stream),
conversion occurs as if by repeatedly calling
[`wcrtomb`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_wchar.html#wcrtomb),
beginning in the
[initial conversion state](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_charset.html#initial%20conversion%20state).
swscanf(L"129E-2", L"%c", &c) stores '1'Copy to clipboard
You write **`%lc`**
to store the matched input characters in an array object,
with elements of type
[wchar_t](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_stddef.html#wchar_t).
If you specify no field width *w,* then *w*
has the value one. The match does not skip leading
[white space](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#white%20space). Any
sequence of *w* characters matches the conversion pattern. For a
[byte stream](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_file.html#byte%20stream),
conversion occurs as if by repeatedly calling
[`mbrtowc`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_wchar.html#wcrtomb), beginning in the
[initial conversion state](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_charset.html#initial%20conversion%20state).
sscanf("129E-2", "%lc", &c) stores L'1'
sscanf("129E-2", "%2lc", &c) stores L'1', L'2'
swscanf(L"129E-2", L"%lc", &c) stores L'1'Copy to clipboard
You write **`%d`**,
**`%i`**,
**`%o`**,
**`%u`**,
**`%x`**, or
**`%X`** to convert
the matched input characters as a signed integer
and store the result in an integer object.
sscanf("129E-2", "%o%d%x", &i, &j, &k) stores 10, 9, 14Copy to clipboard
You write
**`%e`**,
**`%E`**,
**`%f`**,
**`%g`**, or
**`%G`**
to convert the matched input characters as a signed fraction, with
an optional exponent, and store the result in a floating-point object.
sscanf("129E-2", "%e", &f) stores 1.29Copy to clipboard
You write **`%n`**
to store the number of characters
matched (up to this point in the format) in an integer object. The
match does not skip leading
[white space](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#white%20space)
and does not match any input characters.
sscanf("129E-2", "12%n", &i) stores 2Copy to clipboard
You write **`%p`**
to convert the matched input characters as
an external representation of a *pointer to void* and store the
result in an object of type *pointer to void.* The input characters
must match the form generated by the
[`%p`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#%p)
[print conversion specification](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#print%20conversion%20specification).
sscanf("129E-2", "%p", &p) stores, e.g. 0x129ECopy to clipboard
You write **`%s`**
to store the matched input characters in
an array object, followed by a terminating null character. If you
do not specify a field width *w,* then *w* has a large value.
Any sequence of up to *w* non white-space characters matches
the conversion pattern.
sscanf("129E-2", "%s", &s[0]) stores "129E-2"Copy to clipboard
For a
[wide stream](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_file.html#wide%20stream),
conversion occurs as if by repeatedly calling
`wcrtomb` beginning in the
[initial conversion state](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_charset.html#initial%20conversion%20state).
swscanf(L"129E-2", L"%s", &s[0]) stores "129E-2"Copy to clipboard
You write **`%ls`**
to store the matched input characters in
an array object, with elements of type
[wchar_t](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_stddef.html#wchar_t),
followed by a terminating null wide character. If you
do not specify a field width *w,* then *w* has a large value.
Any sequence of up to *w* non white-space characters matches
the conversion pattern. For a
[byte stream](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_file.html#byte%20stream),
conversion occurs as if by repeatedly calling
[`mbrtowc`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_wchar.html#mbrtowc),
beginning in the
[initial conversion state](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_charset.html#initial%20conversion%20state).
sscanf("129E-2", "%ls", &s[0]) stores L"129E-2"
swscanf(L"129E-2", L"%ls", &s[0]) stores L"129E-2"Copy to clipboard
You write **`%[`**
to store the matched input characters in
an array object, followed by a terminating null character. If you
do not specify a field width *w,* then *w* has a large value.
The match does not skip leading
[white space](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#white%20space).
A sequence of up to *w*
characters matches the conversion pattern in the
**scan set** that follows.
To complete the scan set, you follow the left bracket
(`[`) in the conversion specification with a sequence
of zero or more **match** characters, terminated by a right bracket
(**`]`**).
If you do not write a caret (**`^`**)
immediately after the `[`, then each
input character must match *one* of the match
characters. Otherwise, each input character must not match *any*
of the match characters, which begin with the character following
the `^`. If you write a **`]`**
immediately after the `[` or `[^`,
then the `]` is the first match character, not
the terminating `]`. If you write a minus
(**`-`**) as other than the first or last match character,
an implementation can give it special meaning.
It usually indicates a range of characters, in conjunction with the
characters immediately preceding or following, as in
`0-9` for all the digits.)
You cannot specify a null match character.
sscanf("129E-2", "%[54321]", &s[0]) stores "12"Copy to clipboard
For a [wide stream](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_file.html#wide%20stream),
conversion occurs as if by repeatedly calling
[`wcrtomb`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_wchar.html#wcrtomb),
beginning in the
[initial conversion state](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_charset.html#initial%20conversion%20state).
swscanf(L"129E-2", L"%[54321]", &s[0]) stores "12"Copy to clipboard
You write **`%l[`**
to store the matched input characters in
an array object, with elements of type
[wchar_t](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_stddef.html#wchar_t),
followed by a terminating null wide character. If you
do not specify a field width *w,* then *w* has a large value.
The match does not skip leading
[white space](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_prin.html#white%20space).
A sequence of up to *w*
characters matches the conversion pattern in the
[scan set](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_scan.html#scan%20set) that follows.
For a [byte stream](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_lib_file.html#byte%20stream),
conversion occurs as if by repeatedly calling
[`mbrtowc`](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_wchar.html#mbrtowc),
beginning in the
[initial conversion state](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_charset.html#initial%20conversion%20state).
sscanf("129E-2", "%l[54321]", &s[0]) stores L"12"
swscanf(L"129E-2", L"%l[54321]", &s[0]) stores L"12"Copy to clipboard
You write **`%%`**
to match the percent character (`%`).
The function does not store a value.
sscanf("% 0XA", "%% %i", &i) stores 10Copy to clipboard
* * *
See also the
**[Table of Contents](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_index.html#Table%20of%20Contents)** and the
**[Index](https://docs.qualcomm.com/doc/80-N3040-23/topic/_cpp_index.html)**.
*[Copyright](https://docs.qualcomm.com/doc/80-N3040-23/topic/cpp_crit_pjp.html) © 1992-2006by P.J. Plauger and Jim Brodie. All rights reserved.*
Last Published: Oct 06, 2026
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